European patent specification 494454 discloses an apparatus and method for applying non-magnetic and non-conductive toner to an imaging member containing an electrostatic pattern, for ultimately imaging substrates, such as a moving paper web. The system as disclosed therein (the disclosure of which is hereby incorporated by reference herein) utilizes a fluidized bed of toner, a roller system for transferring the toner to an imaging member (the rollers having various electrical potentials), and a mechanism for replenishing the toner in the fluidized bed. While the system described therein is highly useful, there are some circumstances when a simpler system is desired for application of the charged toner to the imaging member, such as in a Moore Business Forms, Inc. (of Lake Forest, Ill.) Midax 300 printing engine, and there are systems in which it is desirable to insure that a uniform mono-layer of toner is undisturbed until the layer is delivered to the imaging member, and any unused toner is returned directly to the toner reservoir. The present invention provides a system for accomplishing these purposes.
According to the present invention in a single component non-magnetic toner applicator system charged toner is delivered to an electrostatic latent image on an imaging member (such as an imaging roller) by a dual conductive roller system. Utilizing electric fields and electrostatic adhesion forces in succession, toner is transported from the reservoir of charged toner to a latent image. The roller system, shields, and vacuum (suction) system according to the invention are configured in such a way that a uniform mono-layer of toner is undisturbed until the layer is delivered to a point in opposition to the latent image on the imaging member, where it subsequently develops the image, and the untransferred residual toner is returned directly to the toner reservoir for reuse. The twin rollers act as a polarity filter for the toner only allowing particularly charged (positively charged in the description provided in the application, but the invention also being applicable to negatively charged systems) to be transferred between the rollers, thus eliminating the adverse affects of having negative toner strain throughout the imaging system. The dual roller system according to the invention also allows great flexibility in delivering the images in a wide variety of positions including the seven o'clock position, the six o'clock position, and essentially any position between about two and ten o'clock, providing a wide variety of possible configurations for a multitude of applications in electrophotography and electrography.
According to one aspect of the present invention a system for the delivery of a substantially uniform mono-layer of toner to an electrostatic latent image on the imaging member is provided comprising the following components: A toner reservoir containing a fluidized bed of charged toner and having a substantially open top. An imaging member. A (e.g. twin) roller delivery system for delivery of a substantially uniform mono-layer of toner to an electrostatic latent image on the imaging member, comprising first and second rollers mounted for rotation about substantially parallel substantially horizontal axes, each roller having a peripheral surface. The first roller positioned so that the peripheral surface thereof receives toner from the substantially open top of the reservoir, and the second roller positioned so that the peripheral surface thereof receives toner from the first roller (e.g. directly from the peripheral surface thereof), and so that the second roller peripheral surface transfers toner directly to the imaging member. Means for charging the first and second rollers to different electrical potentials. Means for rotating the first and second rollers (e.g. in opposite directions of rotation) about the axes. Means for scraping toner from the first roller peripheral surface between the second roller and the reservoir at a portion of the first roller peripheral surface past the second roller in the direction of rotation of the first roller, so that the toner falls into the toner reservoir and does not escape into the surrounding environment. And means for scraping toner from the second roller peripheral surface after transfer of toner therefrom (e.g. to the second roller) so that toner falls into the toner reservoir and does not escape into the surrounding environment.
The toner scraping means may comprise any suitable conventional scraping devices, such as conventional scraper blades (rigid or flexible), or scraper blades associated with gas blasts and/or suction sources, and/or mounted within particular configured shields and housings so as to positively redirect the toner to the toner reservoir.
The means for charging the first and second rollers may be any conventional electrical potential sources. They may charge the rollers so that they are both at positive potentials, typically with the second roller at an electrical potential lower than the first. For example, the charging means may maintain the second roller at a potential that is about 300-500 volts (e.g. about 400 volts) below the first roller. For example, the first roller could be charged to a potential between about 400-500 volts (positive), with the second roller between about 100-700 volts (positive).
Suction means are preferably also provided adjacent the second roller both before and after the second roller peripheral surface transfers toner to the imaging member in the direction of rotation thereof, so as to remove stray toner without disturbing the substantially uniform mono-layer of toner. The suction means may comprise any conventional vacuum source with any desired channels configured to withdraw the stray toner from unwanted positions to a disposal site.
The means for rotating the rollers may comprise any conventional power source including electrical motors, fluid driven motors, belts and pulleys, chains and sprockets, gears or the like. The second roller preferably transfers toner to the imaging member at approximately a seven o'clock position, or at a six o'clock position. Desirably the first roller axis of rotation is both horizontally and vertically spaced from the second roller axis of rotation.
The first and second rollers are preferably positioned and charged by the charging means so that the rollers function as a polarity filter for toner, allowing only particularly charged toner to be transferred from the toner reservoir to the imaging member. The first and second rollers are typically positioned so that there is a gap between them that is of substantial uniform with, e.g. between about 100-250 microns.
According to another aspect of the present invention a system is provided comprising the following components: A toner reservoir containing a bed of charged toner and having a substantially open top. An imaging member. A (e.g. twin) roller delivery system for delivery of a substantially uniform mono-layer of toner to an electrostatic latent image on the imaging member, comprising first and second rollers mounted for rotation about substantially parallel substantially horizontal axes, each roller having a peripheral surface. The first roller positioned so that the peripheral surface thereof receives toner from the substantially open top of the reservoir, and the second roller positioned so that the peripheral surface thereof receives toner from the first roller (e.g. directly from the peripheral surface thereof), and so that the second roller peripheral surface transfers toner directly to the imaging member. Means for charging the first and second rollers to different electrical potentials. Means for rotating the first and second rollers about their axes of rotation. And suction means provided adjacent the second roller both before and after the second roller peripheral surface transfers toner to the imaging member in the direction of rotation thereof, so as to remove stray toner without disturbing the substantially uniform mono-layer of toner. The details of the components preferably are such as described above.
According to yet another aspect of the present invention a system is provided comprising the following components: A toner reservoir containing a fluidized bed of charged toner and having a substantially open top. An imaging member. A twin roller delivery system for delivery of a substantially uniform mono-layer of toner to an electrostatic latent image on the imaging member, consisting of first and second rollers mounted for rotation about substantially parallel substantially horizontal axes, each roller having a peripheral surface. The first roller positioned so that the peripheral surface thereof receives toner from the substantially open top of the reservoir, and the second roller positioned so that the peripheral surface thereof receives toner directly from the first roller peripheral surface, and so that the second roller peripheral surface transfers toner directly to the imaging member. Means for charging the first and second rollers to different electrical potentials. Means for rotating the first and second rollers in opposite directions of rotation about the axes. And wherein the first and second rollers are positioned and charged by the charging means so that the rollers function as a polarity filter for toner, allowing only particularly charged toner to be transferred from the toner reservoir to the imaging member. Preferably, the first and second rollers are positioned so that the axes thereof are both horizontally and vertically offset from each other and so that there is a gap therebetween that has a substantially uniform width between about 100-250 microns. The other details of the system preferably are as described above.
It is the primary object of the present invention to provide a simple yet effective system for the delivery of a uniform mono-layer toner to an electrostatic latent image on an imaging member. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.